This book offers an in-depth historical analysis of the impact of the Crusades on Sunni-Shiite relations, revealing the historical roots of contemporary sectarian tensions. Mohamed El Mokhtar Shinqiti argues that this confrontation with the external other contributed to deepening internal divisions and politicizing theological and jurisprudential disagreements. The book traces the evolution of sectarian discourse during that period and how political powers from both sides exploited this conflict to consolidate their legitimacy. The work is a rigorous study that highlights the intersection of religion and politics in shaping Islamic history.